Downhole tool using a locking clutch

ABSTRACT

A downhole tool may be operated using a locking clutch. The downhole tool may include an upper downhole motor having a rotor. The downhole tool may also include a lower downhole motor having a shaft. Both the rotor and shaft may rotate relative to the housing. The locking clutch may be coupled to the rotor and the shaft, and may transmit a torque from the rotor to the shaft. The locking clutch may include at least one locking pawl configured to move from an engaged position to a disengaged position when the shaft rotates above a disengagement speed. In the engaged position, the upper downhole motor may provide a torque boost to limit sticking or stall of a drill bit coupled to the downhole tool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S. Patent Application Ser. No. 62/017,019 filed Jun. 25, 2014 and titled “Downhole Tool Using a Locking Clutch,” which application is expressly incorporated herein by this reference in its entirety.

BACKGROUND

Drilling tools, including downhole motors, may be used to provide rotational force to a drill bit when drilling earthen formations. Downhole motors used for this purpose may be driven by drilling fluids pumped from surface equipment through a drill string. In use, the drilling fluid may be forced through the downhole motor, which may extract energy from the hydraulic flow to provide rotational force to a drill bit located below the downhole motor. A downhole motor may include a positive displacement mud motor (PDM) or a turbodrill motor.

In some scenarios, an operator may employ the downhole motor to operate with a particular rotating speed and/or torque in order to facilitate the drilling of certain formations. For example, for some turbodrills, the operator may apply an additional weight on bit (WOB) to the drill string in order to lower a rotational speed and to increase an output torque of the turbodrill. In some cases, the lowered rotational speed and increased output torque may lead to a higher mechanical output power and/or rate of penetration (ROP) for the drill bit.

SUMMARY

Described herein are embodiments of various downhole tools using a clutch. In some embodiments, the downhole tool may include a housing having a bore extending throughout and an upper end configured to be coupled to a drill string. The downhole tool may also include an upper downhole motor having an uphole rotor positioned in the bore and configured to rotate relative to the housing. The downhole tool may further include a lower downhole motor having a rotatable shaft positioned in the bore, where the shaft is rotatable relative to the housing and where a downhole end of the shaft is configured to be coupled to a drill bit. The downhole tool may additionally include a locking clutch coupled to the uphole rotor and the shaft, where the locking clutch is configured to transmit a torque from the uphole rotor to the shaft. The locking clutch may include at least one locking pawl configured to engage with an inner diameter of the uphole rotor and an outer diameter of the shaft, where the at least one locking pawl is biased into an engaged position by one or more biasing mechanisms. The at least one locking pawl may also be configured to move to a disengaged position when the shaft rotates at or above a disengagement speed.

In some embodiments, the downhole tool may include a housing having a bore extending throughout and an upper end configured to be coupled to a drill string. The downhole tool may also include a positive displacement mud motor (PDM) having a rotor positioned in the bore and configured to rotate relative to the housing. The downhole tool may further include a turbodrill having a rotatable shaft positioned in the bore, where the shaft is rotatable relative to the housing and where a downhole end of the shaft is configured to be coupled to a drill bit. The downhole tool may additionally include a locking clutch coupled to the rotor and the shaft, where the locking clutch is configured to transmit a torque from the rotor to the shaft. The locking clutch may include at least one locking pawl configured to engage with an inner diameter of the rotor and an outer diameter of the shaft, where the at least one locking pawl is biased into an engaged position by one or more biasing mechanisms. The at least one locking pawl may also be configured to move to a disengaged position when the shaft rotates at or above a disengagement speed.

Described herein are embodiments for a method of using a downhole tool that is tripped into a wellbore. The downhole tool may include a housing having a bore extending throughout and an upper end configured to be coupled to a drill string. The downhole tool may also include an upper downhole motor having an uphole rotor positioned in the bore and configured to rotate relative to the housing. The downhole tool may further include a lower downhole motor having a rotatable shaft positioned in the bore, where the shaft is rotatable relative to the housing and where a downhole end of the shaft is configured to be coupled to a drill bit. The downhole tool may additionally include a locking clutch coupled to the uphole rotor and the shaft, where the locking clutch is configured to transmit torque from the uphole rotor to the shaft. The locking clutch may include at least one locking pawl rotatable between an engaged position and a disengaged position. The method may also include rotating the shaft below a disengagement speed, causing the at least one locking pawl to move to the engaged position and to transmit the torque from the uphole rotor to the shaft.

Another method may include tripping a downhole tool into a wellbore. The downhole tool may include an upper downhole motor, a lower downhole motor, and a clutch coupled to, and optionally positioned between, the upper and lower downhole motors. The clutch can selectively transmit torque from the upper downhole motor to the lower downhole motor. By rotating the shaft above a threshold speed, torque may not be transmitted from the upper downhole motor to the lower downhole motor. By rotating the shaft below the threshold speed, the clutch may transmit torque from the upper downhole motor to the lower downhole motor.

The above referenced summary section is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description section. The summary is not intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to embodiments that solve disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will be described with reference to the accompanying drawings. It should be understood, however, that the accompanying drawings illustrate some of the various embodiments described or contemplated herein, and are not meant to limit the scope of various embodiments described herein.

FIG. 1 is a cross-sectional view of a downhole tool in accordance with embodiments of the present disclosure.

FIG. 2 is a cross-sectional view of a downhole tool including a positive displacement motor (PDM) coupled to a locking clutch in accordance with embodiments of the present disclosure.

FIG. 3 is a cross-sectional view of a downhole tool including a turbodrill coupled to a locking clutch in accordance with embodiments of the present disclosure.

FIG. 4 is a perspective view of a locking clutch in accordance with embodiments of the present disclosure.

FIG. 5 is an exploded view of a locking clutch in accordance with embodiments of the present disclosure.

FIG. 6 is a perspective view of a carrier assembly in accordance with embodiments of the present disclosure.

FIG. 7 is a cross-sectional bottom view of a locking clutch with locking pawls in a disengaged position, in accordance with embodiments of the present disclosure.

FIG. 8 is a cross-sectional bottom view of a locking clutch with locking pawls in an engaged position in accordance with embodiments of the present disclosure.

FIG. 9 is a perspective view of a locking pawl in accordance with embodiments of the present disclosure.

FIG. 10 is a side view of a locking pawl in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings and figures. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and assemblies have not been described in detail so as not to obscure aspects of the disclosed embodiments.

Various embodiments of downhole tools using a locking clutch, and components thereof, will now be described in more detail with reference to FIGS. 1-10. In some embodiments, a downhole tool may be used to drive a bit (e.g., a drill bit, mill, reamer, etc.), where the downhole tool may include multiple downhole motors and a clutch. In the same or other embodiments, the downhole tool may be part of a bottomhole assembly of a drill string. In some embodiments, a clutch may be used to isolate operation of different downhole tools.

A clutch, which may include a locking clutch or a one-way clutch, may couple multiple downhole motors together. An upper downhole motor may be uphole relative to a lower, downhole motor, and the upper downhole motor may be connected to upper members of the drill string. As further described herein, the locking clutch may selectively provide a rotational link between the downhole motors in order to transmit torque from the upper downhole motor to the lower downhole motor. The lower downhole motor may be connected to a drill bit, a mill, a reamer, or other bit, such that the transmitted torque may help to drive the bit in the event that the lower downhole motor stalls or becomes stuck. In particular, as rotational speed is lowered and output torque is increased, the bit may tend to become stalled or stuck due to an increase in friction between the bit and the formation. When such a situation starts to occur, the upper downhole motor may selectively provide rotation, through the locking clutch, to drive the lower downhole motor and/or the bit.

Relative to the lower downhole motor, the upper downhole motor may operate at a low rotational speed and produce a high output torque. In some embodiments and as further described herein, the upper downhole motor may include a PDM. In some embodiments, and relative to the upper downhole motor, the lower downhole motor may operate at a high rotational speed and produce a low output torque. In the same or other embodiments, and as further described herein, the lower downhole motor may be a turbodrill motor.

FIG. 1 is a cross-sectional view of a downhole tool 10 in accordance with some embodiments of the present disclosure. In particular, the downhole tool 10 may include a PDM 100, a locking clutch 200, and a turbodrill 300. The PDM 100 may be positioned uphole relative to the turbodrill 300. As described further herein, the PDM 100 may include a stator and a rotor subassembly 110 within a housing 105 of the PDM 100. Additionally, the turbodrill 300 may include a rotatable shaft 310 within a housing 305 of the turbodrill 300. In some embodiments, the housing 105 and the housing 305 may be coupled together, such as via a pin and/or box connection or any other connection mechanism known to those skilled in the art. In the same or other embodiments, a downhole end portion of the rotor subassembly 110 may be coupled to an uphole end portion of the rotatable shaft 310 via the locking clutch 200.

In operation, and as further described herein, the locking clutch 200 may be configured to engage the PDM 100 and the turbodrill 300 based on a relative rotation between the rotor subassembly 110 and the rotatable shaft 310. In some embodiments, the rotatable shaft 310 may rotate at a higher speed than the rotor subassembly 110.

Due to WOB applied to the drill string, friction generated with a formation, and the like, the rotatable shaft 310 of the turbodrill 300 may begin to slow or cease to rotate. The rotor subassembly 110 may, however, continue to rotate. In such embodiments, the locking clutch 200 may selectively engage the PDM 100 and the turbodrill 300, and apply torque from the rotor subassembly 110 to the rotatable shaft 310. In particular, the locking clutch 200 may apply this torque when the rotational speed of the shaft 310 is less than the rotational speed of the rotor subassembly 110 (i.e., when the relative rotation between the rotor subassembly 110 and the shaft 310 is zero or negative). In such embodiments, the locking clutch 200 may mechanically engage the rotor subassembly 110 with the shaft 310. In doing so, the PDM 100, through the locking clutch 200, may impart rotation to a bit coupled to the shaft 310, thereby increasing torque and/or freeing the bit from being stalled or stuck. The locking clutch 200 and the PDM 100 may therefore act as an anti-stall mechanism for the turbodrill 300. Once the bit is freed, the turbodrill 300 may be able to operate and increase its rotational speed. At that point, the locking clutch 200 may disengage the shaft 310 from the rotor subassembly 110. In some embodiments, the clutch 200 may therefore selectively isolate the bit and/or the turbodrill 300 from the PDM 100. Accordingly, a clutch 200 may be used to isolate various different components to operate independently of one or more other components. In at least some embodiments, a clutch similar to the clutch 200 may further be used to isolate the turbodrill 300 from the bit.

As mentioned herein, relative to the lower downhole motor (e.g., turbodrill 300), the upper downhole motor (e.g., PDM 100) may operate at a low rotational speed and produce a high output torque. In particular, a runaway rotational speed of the upper downhole motor may be lower than runaway rotational speed of the lower downhole motor. The upper downhole motor may also produce a relatively high output torque, such that the upper downhole motor produces a higher output power than the lower downhole motor when operating at their respective runaway rotational speeds.

In some embodiments, as mentioned herein, the upper downhole motor may be the PDM 100. Other embodiments of the upper downhole motor may be used, including other configurations of a PDM. FIG. 2 illustrates a cross-sectional view of the PDM 100 coupled to the locking clutch 200 in accordance with embodiments of the present disclosure. As shown, the housing 105 of the PDM 100 may have an upper connection 102 for engaging with upper members of a drill string. The PDM 100 may also include a stator 104 inside, and optionally coupled to an inner diameter of, the housing 105.

The rotor subassembly 110 may be at least partly within a bore of the stator 104. The rotor subassembly 110 may include a rotor 112, a shaft 114, a lower drive shaft 116, and a downhole connector 118. The rotor subassembly 110 may be oriented such that the rotor 112 may be within the stator 104, and a downhole end portion of the rotor 112 may be coupled to an upper end portion of the shaft 114. In some embodiments, the shaft 114 may be flexible. For instance, the shaft 114 may flex to absorb variation in the positioning of the rotor 112.

A lower end portion of the shaft 114 may be coupled to an upper end portion of the lower drive shaft 116, and a lower end portion of the lower drive shaft 116 may be coupled to an upper end portion of the downhole connector 118. In some embodiments, a lower portion of the downhole connector 118 may be configured to be coupled to the shaft 310 of the turbodrill 300 using the locking clutch 200. In some embodiments, the lower drive shaft 116 and/or the downhole connector 118 may be considered optional pieces of the PDM 100. The PDM 100 may include one or more bearings 120. The bearings 120 may include thrust bearings, radial bearings or the like. In some embodiments, the bearings 120 are configured to transfer an axial load from the rotor subassembly 110 to the housing 105. In some embodiments, the rotor subassembly 110 may be configured to freely rotate relative to the housing 105.

Drilling fluid, e.g., mud, flowing through the housing 105 may cause the rotor subassembly 110 to rotate. In particular, the drilling fluid may flow in the spaces between the stator 104 and the rotor 112. In some embodiments, the PDM 100 may operate according to a reverse mechanical application of the Moineau principle, where pressurized drilling fluid is forced though a series of channels formed on the rotor 112 and the stator 104. The spaces between the stator 104 and the rotor 112 may be generally helical or lobed in shape and may extend the entire length of the stator 104 and the rotor 112. The passage of the pressurized drilling fluid may cause the rotor 112 to rotate within the stator 104. For example, a substantially continuous seal may be formed between the rotor 112 and the stator 104, and the pressurized fluid may act against the rotor 112 proximate the sealing surfaces so as to impart rotational motion on the rotor 112 as the pressurized drilling fluid passes through the helical spaces.

The rotor 112 may impart its rotation to the shaft 114, the lower drive shaft 116, the downhole connector 118, or any combination of the foregoing. As a result, the entire rotor subassembly 110 may rotate. In this manner, the rotor subassembly 110 may provide an output torque for downhole members of the drill string that are directly or indirectly coupled to the downhole connector 118.

Relative to the upper downhole motor (e.g., PDM 100), the lower downhole motor (e.g., turbodrill 300) may operate at a high rotational speed and/or produce a low output torque. In particular, as mentioned herein, a runaway rotational speed of the upper downhole motor may be lower than runaway rotational speed of the lower downhole motor. The lower downhole motor may also produce a relatively low output torque, such that the lower downhole motor produces a lower output power than the upper downhole motor when each operates at its respective runaway rotational speed.

In some embodiments, as mentioned herein, the lower downhole motor may be the turbodrill 300. Other embodiments of the lower downhole motor may be used, including other configurations of a turbodrill. FIG. 3 illustrates a cross-sectional view of the turbodrill 300 coupled to the locking clutch 200 in accordance with embodiments of the present disclosure. As mentioned herein, an uphole end portion of the housing 305 of the turbodrill 300 may be configured to couple to the housing 105. One or more turbine stages (not shown) may be within the housing 305 and may be used to rotate the shaft 310. At a downhole end portion of the turbodrill 300, a bit (not shown) may be attached to the shaft 310 by a downhole connection.

The turbodrill 300 may use turbine stages to provide rotational force to the bit. The turbine stages may include one or more stators and one or more rotors. The one or more stators may include non-moving stator blades, and the rotors may include one or more movable rotor blades. The movable rotor blades may be part of a rotor assembly and may be mechanically coupled to the shaft 310 (e.g., by compression). The turbine stages may be designed such that the blades of the stator stages direct a flow of drilling fluid into corresponding rotor blades to provide rotation to the shaft 310, where the shaft 310 ultimately couples to and drives the bit. Thus, the drilling fluid flowing into the rotor blades may cause the rotor and the bit to rotate with respect to the housing 305. The turbodrill 300 may include thrust and/or radial bearings (not shown). For instance, radial bearings may be provided between the shaft 310 and the housing 305 to help maintain the shaft 310 concentric within the housing 305.

While providing rotational force to the shaft 310, the turbine stages may also produce a downhole axial force, or thrust, from the drilling fluid. The downhole thrust, however, may produce a higher WOB than used for operation of the turbodrill 300. To mitigate the effects of excess thrust in the turbodrill 300, thrust bearings may be provided. The thrust bearings may include steel roller bearings, polycrystalline diamond compact (PDC) surface bearings, other bearings known to those skilled in the art, or any combination of the foregoing. A portion of the turbodrill 300 in which the thrust bearings and the radial bearings are located may be called a bearing section. In addition, stabilizers (not shown) may be coupled to the housing 305 to help maintain the turbodrill 300 centered within a wellbore. In some embodiments, the shaft 310 may include a power shaft, a flexible shaft, an upper drive shaft similar to the lower drive shaft 116, other shafts or components, or some combination of the foregoing.

As discussed herein, the locking clutch 200 may be used to couple the upper end portion of the shaft 310 to the lower end portion of the rotor subassembly 110. In particular, the locking clutch 200 may couple the upper end portion of the shaft 310 to a downhole portion of the downhole connector 118.

FIGS. 4 and 5 are perspective and exploded views, respectively, of an example locking clutch 200 in accordance with embodiments of the present disclosure. The locking clutch 200 may or may not be the same as the locking clutch 200 of FIGS. 1 and 3 for use in selectively engaging a shaft of a lower downhole motor (e.g., shaft 310 of the turbodrill 300 of FIG. 3) with a component of an upper downhole motor (e.g., rotor subassembly 110 of the PDM 100 of FIG. 2) The locking clutch 200 may include a carrier assembly 206 coupled to (e.g., mounted on) a shaft 310. The carrier assembly 206 may include of one or more cylindrical pieces configured to engage with the shaft 310. Further, one or more keys 207 may be inserted between the carrier assembly 206 and the shaft 310 to rotationally lock the carrier assembly 206 in place upon the shaft 310.

The carrier assembly 206 may include one or more locking pawls 208. In the illustrated embodiment, the one or more locking pawls 208 may include multiple locking pawls 208 circumferentially or angularly spaced about the carrier assembly 206. The locking pawls 208 may be configured to engage a plurality of recesses 210 formed on an outer diameter of the shaft 310. The locking pawls 208 may be coupled to the carrier assembly 206 by any suitable method. In some embodiments, the locking pawls 208 may be coupled to the carrier assembly 206 in a manner that allows each locking pawl 208 to rotate about a pivot axis 212. In some embodiments, cylindrical side pins 216 may be inserted and locked in corresponding openings 220 formed in the carrier assembly 206.

Biasing members 214 may be positioned between the side pins 216 of each locking pawl 208 and the carrier assembly 206, thereby biasing the locking pawls 208 inwardly towards the recesses 210. When the locking pawls 208 are biased such that they become engaged with the corresponding recesses 210 formed in the shaft 310, the locking pawls 208 may be said to be in an “engaged” position. As further explained herein, with the locking pawls 208 in the engaged position, the locking clutch 200 may couple the rotor subassembly 110 to the shaft 310.

A carrier end plate 234 may, in some embodiments, be engaged behind the carrier assembly 206 and the locking pawls 208, such that the carrier end plate 234 may lock the locking pawls 208 into the carrier assembly 206. As such, the carrier end plate 234 may include corresponding openings 220 to receive the cylindrical side pins 216 of the locking pawls 208. Additionally, one or more stop pins 224 may extend between the carrier end plate 234 and the carrier assembly 206 to restrict or even prevent the locking pawls 208 from rotating too far about a pivot axis 212. In some embodiments, the carrier assembly 206 may not be used, and the shaft 310 may be configured to include the one or more locking pawls 208.

In some embodiments, the cylindrical side pins 216 may not be inserted in the openings 220. Rather, the locking pawls 208 may be inserted in the carrier assembly 206, such that the cylindrical side pins 216 may be proximate an inner surface of the carrier assembly 206. FIG. 6 illustrates a perspective view of the carrier assembly 206 in accordance with embodiments of the present disclosure. As shown, the locking pawls 208 may include at least one extension portion 209 on at least one side of the locking pawl 208. The extension portion 209 may be configured to engage with a corresponding undercut 211 formed on an inside diameter of the carrier assembly 206. Thus, in such embodiments, the locking pawls 208 may move about at least two pivot axes (e.g., axes A and B in FIG. 10) within the carrier assembly 206, as further described herein. Engaging the extension portion 209 with the corresponding undercut 211 may limit the rotation of a locking pawl 208 within the carrier assembly 206, thereby restricting or even preventing over-rotation of the locking pawl 208.

Returning to FIG. 5, the biasing members 214 may be torsion springs that are, in some embodiments, positioned around the side pins 216. Cutouts 222 in the carrier end plate 234 may be formed to direct the flow of drilling fluid across the locking pawls 208, such that the fluid flow assists in biasing the locking pawls 208 inward toward an “engaged” position further described herein. Back sides of the locking pawls 208 may similarly be configured to divert a longitudinal or axial flow of the drilling fluid across the back sides, thereby creating a radial force.

In some embodiments, the biasing members 214 may bias the locking pawls 208 toward the engaged position with a predetermined torque provided by the biasing members 214. In particular, as the shaft 310 rotates at a relatively low rotational speed, a spring force of the biasing members 214 may urge a leading end 232 (see FIG. 7) of the locking pawls 208 into corresponding recesses 210 on the shaft 310. In addition, the spring or other biasing force may urge trailing ends 240 (see FIG. 7) into contact with locking notches 242 on an inner diameter 218 of the downhole connector 118. In such embodiments, when the ends of the locking pawls 208 are biased into contact with the recesses 210 and the locking notches 242, the locking pawls 208 may be said to be in the engaged position.

With the locking pawls 208 in the engaged position, the locking notches 242 may act as cam surfaces to mechanically drive the locking pawls 208 and, in turn, the recesses 210. In this manner, the locking clutch 200 may be said to be “engaged,” in that it couples the PDM 100 to the turbodrill 300, such that the rotor subassembly 110 can be used to drive and/or apply its output torque to the shaft 310. Accordingly, at low speeds, the locking pawls 208 can function as a ratchet mechanism, in that the pawls 208 can transition between the engaged position and the disengaged position further described herein.

Each locking pawl 208 may have a mass center, generally indicated at M. The mass center M may be offset by a distance D (see FIG. 10) with respect to the pivot axis 212. Rotation of the shaft 310 may create a centrifugal force that acts on the mass center M. As the mass center M may be offset from the pivot axis 212 or the pivot axis B (see FIG. 10), the centrifugal force may cause a torque to be applied to the locking pawls 208. This torque may be in the opposite direction of the torque applied by biasing members 214.

In some embodiments, as the speed of rotation of the shaft 310 increases, the centrifugal force acting on each locking pawl 208 at the mass center M may increase, and the resulting torque may increase correspondingly. When the resulting torque acting on each locking pawl 208 overcomes the torque created by a biasing force of the biasing members 214, the locking pawls 208 may then no longer be urged into contact with the locking notches 242 of the inner diameter 218.

At that point, the locking pawls 208 may be said to be in the “disengaged” position. Thus, the locking clutch 200 may be disengaged through centrifugal action, as opposed to a mechanical, ratcheting action. The centrifugal force may be defined by:

F _(centrifugal) =M·r·ω ²  (Equation 1)

where M is the mass of the pawl, r is distance from the mass center of the pawl to the center of a shaft (e.g., a turbine shaft), and w is the rotational velocity of the shaft. The stop pin 224 may restrict or even prevent the locking pawls 208 from centrifugally rotating too far out of disengagement with recesses 210. The torque resulting from centrifugal force may be defined by:

T _(centrifugal) =F _(centrifugal) ·D  (Equation 2).

With the locking pawls 208 in the disengaged position, the ends of the locking pawls 208 may no longer be in contact with the recesses 210 and the locking notches 242. In this manner, the locking clutch 200 may be said to be “disengaged,” in that it no longer couples the upper downhole motor (e.g., PDM 100 of FIG. 2) to the lower downhole motor (e.g., turbodrill 300 of FIG. 3), as the rotor subassembly (e.g., rotor subassembly 110) may be unable to drive and/or apply its output torque to the shaft 310. Additional details about an example locking clutch 200 may be found in U.S. Pat. No. 8,776,915, which is incorporated herein by this reference in its entirety.

FIG. 7 is a cross-sectional bottom view of the locking clutch 200 with the locking pawls 208 in the disengaged position, and FIG. 8 is a cross-sectional bottom view of the locking clutch 200 with the locking pawls 208 in the engaged position in accordance with embodiments of the present disclosure.

In some embodiments, the rotor subassembly 110 of an upper downhole motor, and the downhole connector 118 in particular, may rotate as indicated by arrow S in response to drilling fluid flowing through the housing 105 (shown in FIG. 2). With the locking pawls 208 in the disengaged position as shown in FIG. 7, the downhole connector 118 may not be coupled to the shaft 310.

Accordingly, at this point, the downhole connector 118 and other components of the rotor subassembly 110 may freely rotate within the housing of the upper downhole motor (e.g. housing 105 of the PDM 100 of FIG. 2), as the downhole connector 118 is not coupled to downhole members of a drill string. As such, the rotor subassembly 110 may be operating at its runaway rotational speed. As an example, this runaway rotational speed may be between 50 and 500 revolutions per minute (RPM). More particularly, the runaway rotational speed may be within a range that includes lower and/or upper limits that include 50 RPM, 100 RPM, 150 RPM, 200 RPM, 250 RPM, 300 RPM, 400 RPM, 500 RPM, and any values therebetween. For instance, the runaway rotational speed may be between 100 and 300 RPM or between 150 RPM and 250 RPM. In other embodiments, the runaway rotational speed may be less than 50 RPM or greater than 500 RPM. Further, while the rotor subassembly 110 may be capable of producing a relatively high torque, the disengagement of the locking clutch 200 may mean that no output torque or output power is applied to a bit of the drill string. In such a scenario, the upper downhole motor may experience a minimal pressure drop.

The shaft 310 of the turbodrill 300 may rotate as indicated by arrow R. During a drilling, milling, reaming, or other downhole operation, the rotation S may be lower in angular velocity as compared to the rotation R. In such embodiments, the shaft 310 may have a higher rotational speed than the rotor subassembly 110. In further embodiments, the shaft 310 may be operating at a nominal rotational speed. The nominal rotational speed may, in some embodiments, be equal to approximately one-half of the runaway rotational speed of the shaft 310. For example, the nominal rotational speed may be about 1500 RPM, and the runaway rotational speed of the shaft 310 may be about 3000 RPM. When operating at the nominal rotational speed, the shaft 310 may be supplying an increased and potentially maximum output power to the bit. At the nominal rotational speed, the torque supplied by the shaft 310 to the bit may be relatively low. For instance, the torque may be about 500 foot-pounds (ft-lbs) (680 N·m). The turbodrill 300 may further experience a pressure drop of about 2000 pounds per square inch (psi) (13.8 MPa).

The values above for nominal rotational speed, runaway rotational speed, torque, and pressure drop are merely illustrative and may be varied in other embodiments. For instance, in some embodiments, the nominal rotational speed may be between 500 RPM and 3000 RPM. More particularly, the nominal rotational speed may be within a range that includes lower and/or upper limits that include any of 500 RPM, 1000 RPM, 1500 RPM, 2000 RPM, 2500 RPM, 3000 RPM, or any values therebetween. In other embodiments, the nominal rotational speed may be less than 500 RPM or greater than 3000 RPM. Similarly, the runaway rotational speed of the shaft 310 may be between 1000 RPM and 6000 RPM. More particularly, the runaway rotational speed of the shaft 310 may be within a range that includes lower and/or upper limits that include any of 1000 RPM, 2000 RPM, 3000 RPM, 4000 RPM, 5000 RPM, 6000 RPM, and any values therebetween. In other embodiments, the runaway rotational speed of the shaft 310 may be less than 1000 RPM or greater than 6000 RPM.

Moreover the torque provided to the bit may be, in some embodiments, between 100 ft-lbs (135 N·m) and 2000 ft-lbs. (2710 N·m). More particularly, the torque may be within a range that includes lower and/or upper limits that include any of 100 ft-lbs (135 N·m), 250 ft-lbs (340 N·m), 500 ft-lbs (680 N·m), 750 ft-lbs (1015 N·m), 1000 ft-lbs (1355 N·m), 1500 ft-lbs (2035 N·m), 2000 ft-lbs (2710 N·m), and any values therebetween. In other embodiments, the torque may be less than 100 ft-lbs (135 N·m) or greater than 2000 ft-lbs (2710 N·m). Additionally, the pressure drop may be between 500 psi (3.4 MPa) and 4000 psi (27.6 MPa). More particularly, the pressure drop may be within a range including lower and/or upper limits that include any of 500 psi (3.4 MPa), 1000 psi (6.9 MPa), 1500 psi (10.3 MPa), 2000 psi (13.8 MPa), 2500 psi (17.2 MPa), 3000 psi (20.7 MPa), 3500 psi (24.1 MPa), 4000 psi (27.6 MPa), and any values therebetween. In other embodiments, the pressure drop may be less than 500 psi (3.4 MPa) or greater than 4000 psi.

As shown in FIGS. 4 and 5, the locking pawls 208 may initially be in the engaged position, where the biasing members 214 may bias the locking pawls 208 toward the engaged position in corresponding locking notches 242 formed in the downhole connector 118. As the rotational speed of the shaft 310 increases in the direction R, the centrifugal force acting on the mass center M about the pivot axis 212 of the locking pawls 208 may increase in accordance with Equation 1 shown above. Once the rotational speed of the shaft 310 is greater than or equal to a predetermined speed, the centrifugal force acting on the mass center M of the locking pawls 208 may become greater than the spring force of the biasing members 214 which may bias the locking pawls 208 toward the engaged position. This predetermined speed may be the rotational speed at which the locking pawl 208 and, in turn the locking clutch 200, may disengage. This rotational speed may be referred to as a disengagement speed. Thus, at rotational speeds greater than or equal to the disengagement speed, the locking pawls 208 may rotate outwardly about the pivot axis 212, and the trailing edges 240 may disengage with the inner diameter 218 of the downhole connector 118.

In some embodiments, the biasing members 214 may be selected so that locking pawls 208 will disengage with the locking notches 242 once the shaft 310 has a rotational speed that is greater than or equal to the disengagement speed. Further, the geometry and material properties (e.g., the density) of the locking pawls 208 may be varied to achieve the same. Particularly, the magnitude and location of mass center M with respect to pivot axis 212 may be varied so that the locking pawls 208 will disengage with the locking notches 242 once the shaft 310 reaches the disengagement speed. For example, a high-density material (e.g., carbides such as tungsten carbide, niobium carbide, titanium carbide, etc.), may be used to manufacture the locking pawls 208 in order to increase their mass.

In some embodiments, as shown in FIGS. 6, 9, and 10, the biasing members 214 may bias the locking pawls 208 toward the engaged position in corresponding locking notches 242 formed in the downhole connector 118 (see FIG. 8). FIGS. 9 and 10 are perspective and side views, respectively, of a locking pawl 208 in accordance with embodiments of the present disclosure. As the rotation speed of the shaft 310 increases in the direction R, the centrifugal force acting on the mass center M may increase in accordance with Equation 1 shown above. In these embodiments, however, the locking pawls 208 pivot about various pivot axes. Thus, the pivot axis may be referred to herein as a dynamic pivot axis. At low speeds, the locking pawl 208 may rotate about a pivot axis A. In such embodiments, the pivot axis A may correspond to a line of contact between the leading edge 232 of the locking pawl 208 and the shaft 310.

In some embodiments, once the speed of the shaft 310 is greater than or equal to the disengagement speed, the centrifugal force acting on the mass center M of the locking pawls 208 may exceed the spring force or other biasing force of the biasing members 214. The leading edge 232 of the locking pawls 208 may move radially outward until extension portions 209 contact the undercuts 211 in the carrier assembly 206. Once the extension portions 209 contact the undercuts 211, the locking pawl 208 may rotate about the line of contact, identified as pivot axis B, between the extension portion 209 and the undercut 211. Thus, at speeds greater than or equal to the disengagement speed, the locking pawls 208 may rotate outward about the pivot axis B, and the trailing edges 240 may disengage with the inner diameter 218 of the downhole connector 118. In such embodiments, a pivot axis of the pawl 208 may move or change, thereby allowing more movement of the locking pawl 208 within the carrier assembly 206 and restricting or even preventing engagement loads from being transmitted to the carrier assembly 206. In some embodiments, the locking pawl 208 may move about any number of pivot axes, depending on the geometries of the locking pawl 208, the carrier assembly 206, the extension portions 209, and the like.

In some embodiments, and as shown in FIG. 8, the rotor subassembly 110 of an upper downhole motor, and the downhole connector 118 in particular, may rotate as indicated by arrow S. In addition, the shaft 310 of the turbodrill 300 may rotate as indicated by arrow R.

In the event the bit (not shown) becomes stuck, slows in rotational speed, or approaches a stall condition, the locking clutch 200 may engage. When the locking clutch 200 is engaged, the locking clutch 200 may allow the transmission of torque from the rotor subassembly 110 to the shaft 310 to drive the bit through a formation, as further described herein. As the rotational speed of the shaft 310 slows, the centrifugal force acting on the locking pawls 208 may decrease. When the rotational speed of the shaft 310 slows to less than the disengagement speed, the torque resulting from the centrifugal force may become less than the torque from the biasing members 214. In some embodiments, the disengagement speed may be equal to the runaway rotational speed of the rotor subassembly 110. For example, the disengagement speed may be about 200 RPM. Accordingly, the locking pawls 208 may rotate around their respective pivot axes (e.g., axis 212 in FIG. 5 or axes A and B in FIG. 10) due to the biasing force of the biasing members 214, thereby urging the trailing end 240 of the locking pawls 208 into contact with the locking notches 242 on the inner diameter 218. The disengagement speed of 200 RPM is merely illustrative, and in some embodiments may be between 50 RPM and 500 RPM. More particularly, the disengagement speed may be within a range that includes lower and/or upper limits that include any of 50 RPM, 100 RPM, 150 RPM, 200 RPM, 250 RPM, 300 RPM, 400 RPM, 500 RPM, and any values therebetween. For instance, the disengagement speed may be between 100 and 300 RPM or between 150 RPM and 250 RPM. In other embodiments, the disengagement speed may be less than 50 RPM or greater than 500 RPM.

As the shaft 310 continues to slow and the leading edges 232 of the locking pawls 208 move into corresponding recesses 210, the trailing ends 240 of the locking pawls 208 may extend radially outward into contact (e.g., ratchet) with the locking notches 242. At this point, the upper downhole motor and its rotor subassembly 110 may act as a drive mechanism for the lower downhole motor and its shaft 310.

The locking pawls 208 may be constructed such that the trailing ends 240 of the locking pawls 208 do not interfere with rotation of the shaft 310 when the shaft 310 is rotating faster than the rotor subassembly 110. Once the rotational speed of the shaft 310 slows to less than the disengagement speed, however, the locking pawls 208 may transition to their engaged positions, and the rotational force (i.e., torque) may then be transferred from the rotor subassembly 110 to the shaft 310 along a load path 250 extending through the locking pawls 208. The locking pawls 208 may be configured such that the load path 250 extends substantially straight through the locking pawl 208 with little to no bending or shear loads.

In some embodiments, once the locking pawls 208 and, in turn, the locking clutch 200 are engaged, the rotor subassembly 110 may no longer be able to freely rotate within the housing (e.g. housing 105 of FIG. 2) of the upper downhole motor. As such, the rotor subassembly 110 may be operating at less than its runaway rotational speed. In some embodiments, this rotational speed may be about 100 RPM. The output torque being transferred by the locking clutch 200 from the rotor subassembly 110 to the shaft 310 may be relatively high. In some embodiments, the total torque being transferred to the drill bit may be the sum of the respective output torques of the rotor subassembly 110 and the shaft 310. In some such embodiments, the total torque may be about 1000 ft-lbs (1355 N·m). In other embodiments, the upper downhole motor may experience a pressure drop of about 200 psi (1.4 MPa). As will be appreciated in view of the disclosure herein, the total torque and pressure drop values presented above are merely illustrative. In other embodiments, for instance, the total torque may be between 500 ft-lbs (680 N·m) and 3000 ft-lbs (4065 N·m). In other embodiments, the total torque may be less than 500 ft-lbs (680 N·m) or grater than 3000 ft-lbs (4065 N·m). The pressure drop may be between 100 psi (0.7 MPa) and 500 psi (3.5 MPa), but in other embodiments may be less than 100 psi (0.7 MPa) or greater than 500 psi (3.5 MPa).

Further, the shaft 310 may have a lower rotational speed than the rotor subassembly 110, and the rotational speed may be less than the nominal rotational speed. In some embodiments, with the locking clutch 200 engaged, the rotational speed of the shaft 310 may be approximately the same as the rotational speed of the rotor subassembly 110. For example, this rotational speed may be about 100 RPM (or between 50 RPM and 500 RPM). In such embodiments, the turbodrill 300 may experience a pressure drop that is less than the pressure drop of the turbodrill 300 when the locking clutch 200 is disengaged. For instance, the pressure drop may be about 1700 psi (11.7 MPa) as compared to about 2000 psi (13.8 MPa) when the locking clutch 2000 is disengaged.

Various embodiments described herein with respect to FIGS. 1-10 may facilitate the drilling or reaming of certain formations, the milling of casing, or other downhole operations. As mentioned herein, for some downhole motors such as a turbodrill 300, an operator may apply additional WOB to the drill string in order to lower a rotational speed and to increase an output torque. In such an event, the lowered rotational speed and increased output torque may lead to the bit becoming stalled or stuck, such as due to an increase in friction between the bit and the downhole formation. Some embodiments described herein may, however, limit or even prevent the bit from becoming stalled or stuck. In some embodiments, a locking clutch may be engaged before the bit becomes stalled or stuck, such as where the locking clutch is configured to have a disengagement speed that is greater than the rotational speed at which the bit stall or nearly stalls. For instance, in the event the bit becomes stuck or slows in rotational speed, the locking clutch may automatically engage and transmit torque from an upper downhole motor (such as from rotor subassembly 110) to a lower downhole motor (such as to the shaft 310) to drive the bit coupled to the lower downhole motor through a formation. Once the bit is freed, the lower downhole motor may be able to operate and increase its rotational speed. At that point, the locking clutch may automatically disengage.

The discussion herein is directed to certain specific embodiments. It is to be understood that the discussion herein is for the purpose of enabling a person with ordinary skill in the art to make and use any subject matter defined now or later by the claims found in any issued patent herein. It is specifically intended that the claims not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.

It will also be understood that, although the terms “first”, “second,” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first object could be termed a second object, and, similarly, a second object could be termed a first object, without departing from the scope of the claims. The first object and the second object are both objects, respectively, but they are not to be considered the same object.

The terminology used in the description of the present disclosure herein is for the purpose of describing particular embodiments and is not intended to be limiting of the present disclosure. As used in the description of the present disclosure and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses one or more possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes” and/or “including,” or the terms “comprise” or “comprising” when used in this specification or claims, specify the presence of stated features, elements, operations, or components, but do not preclude the presence or addition of one or more other features, elements, operations, components, and groups thereof.

As used herein, relational terms such as “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; “below” and “above”; and other similar terms indicating relative positions above or below a given point or element may be used in connection with some embodiments described or illustrated herein. When applied to equipment and methods for use in wellbores that are deviated or horizontal, when applied to equipment and methods that when arranged in a wellbore are in a deviated or horizontal orientation, or when arranged outside of a wellbore, such terms may refer to a left to right, right to left, or other relationships as appropriate. While embodiments of the present disclosure may be used in a wellbore used for the exploration or production of oil, gas, or other hydrocarbons, in other embodiments the wellbore may be used for other purposes (e.g., water production and exploration, utility line placement, etc.). Further, embodiments of the present disclosure may be used outside of a wellbore in some embodiments, including within aerospace, automotive, manufacturing, or other industries. For instance, a mill or drill bit may be used in a manufacturing system to form a bore within a particular material, and motors, clutches, and the like as arranged herein may be used to rotate and drive the dill bit or mill.

Ranges of values presented herein may include a list of potential lower and/or upper values for the range. It is intended that any value may be used alone to identify a particular value or an open-ended range (e.g., 500 RPM, up to 500 RPM, at least 500 RPM), or as an upper or lower limit in a closed-ended range. All numerical values referenced or claimed herein are “about” or “approximately” that value. Such values include at least the statistical variations, manufacturing tolerances, and the like as would be expected by one of ordinary skill in the art to achieve a same or similar function or result.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be devised without departing from the basic scope thereof, which may be determined by the claims that follow. Although the subject matter has been described in language specific to structural features and/or operations or methods, it is to be understood that the subject matter defined in the appended claims is not limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. 

What is claimed is:
 1. A downhole tool, comprising: a housing having an upper end portion configured to be coupled to a drill string; an upper downhole motor having a rotor configured to rotate relative to the housing; a lower downhole motor having a shaft, the shaft being rotatable relative to the housing, the shaft being configured to be coupled to a bit; and a locking clutch coupled to the rotor and the shaft, the locking clutch being configured to selectively transmit a torque from the rotor to the shaft, the locking clutch including: at least one locking pawl configured to engage with an inner diameter of the rotor and an outer diameter of the shaft, the at least one locking pawl being biased into an engaged position, and the at least one locking pawl being configured to be in a disengaged position when the shaft rotates above a disengagement speed and in an engaged position when the shaft rotates below the disengagement speed.
 2. The downhole tool of claim 1, the locking clutch being configured to use the at least one locking pawl to selectively transmit the torque from the rotor to the shaft when the at least one locking pawl is in the engaged position.
 3. The downhole tool of claim 1, the at least one locking pawl being biased into the engaged position when the shaft rotates below the disengagement speed.
 4. The downhole tool of claim 1, the at least one locking pawl being configured to be biased into the disengaged position by a centrifugal force when the shaft is rotated above the disengagement speed.
 5. The downhole tool of claim 1, the inner diameter of the rotor including a plurality of locking notches configured to receive a trailing end of the at least one locking pawl when the at least one locking pawl is in the engaged position.
 6. The downhole tool of claim 1, the outer diameter of the shaft including a plurality of recesses configured to receive a leading end of the at least one locking pawl when the at least one locking pawl is in the engaged position.
 7. The downhole tool of claim 1, the at least one locking pawl being biased into the engaged position by one or more biasing mechanisms positioned between the at least one locking pawl and a carrier assembly coupled to the outer diameter of the shaft.
 8. The downhole tool of claim 1, the at least one locking pawl being configured to rotate from the engaged position to the disengaged position about at least one pivot axis.
 9. The downhole tool of claim 1, the upper downhole motor being configured to have runaway rotational speed that is lower than a runaway rotational speed of the lower downhole motor.
 10. The downhole tool of claim 1, the locking clutch being configured to selectively transmit the torque from the rotor to the shaft to prevent a stall condition of the shaft.
 11. The downhole tool of claim 1, the disengagement speed being equal to a runaway rotational speed of the upper downhole motor.
 12. The downhole tool of claim 1, the upper downhole motor including a positive displacement motor, and the rotor including a rotor subassembly.
 13. The downhole tool of claim 1, the lower downhole motor including a turbodrill.
 14. A drilling tool, comprising: a housing; a positive displacement motor coupled to the housing, the positive displacement motor including a rotor configured to rotate relative to the housing; a turbodrill having a shaft that is rotatable relative to the housing; a locking clutch between the positive displacement motor and the turbodrill, the locking clutch being configured to selectively transmit a torque from the rotor to the shaft, the locking clutch including at least one locking pawl configured to engage the rotor and the shaft when in an engaged position, and to disengage at least one of the rotor or the shaft when in a disengaged position as a result of the shaft rotating at or above a disengagement speed; and a drill bit coupled to the shaft of the turbodrill.
 15. The drilling tool of claim 15, the locking clutch being configured to selectively transmit the torque from the rotor to the shaft when the at least one locking pawl is in the engaged position.
 16. The drilling tool of claim 15, the at least one locking pawl being biased by one or more biasing mechanisms into the engaged position when the shaft rotates below the disengagement speed, and biased by a centrifugal force into the disengaged position when the shaft rotates above the disengagement speed.
 17. The drilling tool of claim 15, an inner diameter of the rotor including a plurality of locking notches configured to receive a trailing end of the at least one locking pawl when the at least one locking pawl is in the engaged position, and an outer diameter of the shaft including a plurality of recesses configured to receive the at least one locking pawl in the engaged position.
 18. A method, comprising: tripping a downhole tool into a wellbore, the downhole tool including an upper downhole motor, a lower downhole motor, and a clutch coupled to, and positioned between, the upper and lower downhole motors, the clutch being configured to selectively transmit torque from the upper downhole motor to the lower downhole motor; rotating a shaft of the lower downhole motor above a threshold speed and, in response, not transmitting torque of the upper downhole motor to the lower downhole motor; and rotating the shaft below the threshold speed and, in response, using the clutch to transmit torque from the upper downhole motor to the lower downhole motor.
 19. The method of claim 18, wherein: the upper downhole motor has a rotor; the lower downhole motor has a rotatable shaft; and the clutch is a locking clutch and includes at least one locking pawl that is rotatable between an engaged position in which the locking clutch transmits torque between the rotor and the shaft and a disengaged position in which the locking clutch does not transmit torque between the rotor and the shaft.
 20. The method of claim 19, wherein the threshold speed is a disengagement speed and the locking pawl has at least two axes of rotation, and wherein: rotating the shaft above the disengagement speed causes the at least one locking pawl to be in the disengaged position; and rotating the shaft below the disengagement speed causes the at least one locking pawl to move to the engaged position and to transmit the torque from the rotor to the shaft. 